Systematic Uncertainty of Radiation Efficiency Based on Some Formulas for Wheeler Method

In evaluating the performance of the small antenna, one of the most important parameters is the radiation efficiency as well as the radiation power. If the input power of the antenna is measured, the radiation power can be determined by multiplying the radiation efficiency by the input power. One of the techniques for measuring the radiation efficiency is the pattern integral method which needs a long measurement time for raising its precision. On the other hand, the Wheeler method is a technique which needs a short measurement time because of requiring reflection coefficients of the antenna under test in free space and shielding which can suppress the radiation from the antenna. However, the Wheeler method faces the problem of having some dips in the efficiency We have studied some solutions of avoiding the dips. However, the uncertainty of the Wheeler method has been hardly reported, as far as the authors know. In this paper, we tried to assess systematic uncertainty of some formulas for evaluating the radiation efficiency of the small antenna using the Wheeler method. As the evaluation formulas are analytically described, the systematic uncertainty for the formulas can be analytically evaluated, too. In this paper, we showed the expressions for the systematic uncertainty. Then, the systematic uncertainty was assessed by using the measured reflection coefficients in free space and the shielding. We discussed the relationship between the measured efficiency and uncertainty.